Journal of Applied Chemical Science International
9(2): 104-114, 2018 ISSN: 2395-3705 (P), ISSN: 2395-3713 (O)
RHEOLOGICAL CHARACTERISTICS OF PETROLEUM JELLY FORMULATIONS CONTAINING ORGANICALLY MODIFIED LAYERED DOUBLE HYDROXIDES
DAMODAR MOSANGI1,2,3, SREEJARANI KESAVAN PILLAI1*, LUMBIDZANI MOYO1 AND SUPRAKAS SINHA RAY1,2 1DST/CSIR National Centre for Nanostructured Materials, Council for Scientific and Industrial Research, 0001, Pretoria, South Africa. 2Department of Applied Chemistry, University of Johannesburg, Droonfontein 2028, Johannesburg, South Africa. 3AMKA Products Pty Limited, Innovation Building, 14 Ellman Street, Sunderland Ridge, Centurion 0157, Pretoria, South Africa.
AUTHORS’ CONTRIBUTIONS This work was carried out in collaboration between all authors. Author DM designed the study, performed the experimental work and wrote the protocols. Authors SKP and LM managed the analyses, managed literature and wrote the first draft of the manuscript. Suprakas Sinha Ray reviewed and corrected the manuscript. All authors read and approved the final manuscript.
ARTICLE INFORMATION Editor(s): (1) Nagatoshi Nishiwaki, Kochi University of Technology, Japan. (2) Ling Bing Kong, Nanyang Technological University, Singapore. Reviewers: (1) Ayi A. Ayi, Federal University, Nigeria. (2) Joel Obed Herrera Robles, Autonomous University of Ciudad Juarez, Mexico. (3) Margarita Teutli León, Benemerita Universidad Autónoma de Puebla (BUAP), Mexico.
Received: 04 June 2018 Accepted: 20 August 2018 Published: 08 September 2018 Original Research Article ______
ABSTRACT
The effectiveness of stearic acid modified layered double hydroxides (OLDH) as viscosity modifier and stabilizer in petroleum jelly (PJ) formulations has been studied and its rheological properties evaluated. Mg-Al- LDH was organically modified using stearic acid which is anionic surfactant widely used in topical formulations. Successful incorporation of stearate anion into LDH interlayers was confirmed by XRD, FTIR, SEM, and TGA results. PJ formulations were prepared using different OLDH contents (0.5, 1, 1.5 and 2 wt. %) using a high shear mixer. The incorporation of OLDH significantly increased the viscosity of the PJ formulations which is explained by strong interaction between OLDH particles and hydrocarbon chains of PJ. The percolation threshold was observed to be at 1.5 wt.% of OLDH loading suggesting the presence of a well- developed interface between the filler and the polymer matrix. The non-Newtonian shear thinning indicated the formation of gel-like structure. Dynamic state rheological data of PJ formulations showed a dominance of elastic property imparted by solid phase in OLDH based system. OLDH, therefore, showed great promise as an efficient structural ingredient in cosmetic formulations offering viscosity enhancement as well as shear thinning behaviour which could result in formulation stability, better skin feel and spreadability. ______
*Corresponding author: Email: [email protected];
Mosangi et al.; JACSI, 9(2): 104-114, 2018
Keywords: Layered double hydroxide; organically modified layered double hydroxides; characterization; petroleum jelly; rheological properties.
1. INTRODUCTION describes topical compositions containing solid starch and hydrophobic starch. The invention claims that the Petrolactum (petroleum jelly (PJ) or Vaseline) is one inclusion of hydrophobic starch reduces the greasy of the ancient skin treatment products and are widely appearance and its resistance to washing although the used in cosmetics and pharmaceuticals industries [1]. rheological property of the formulation was not In pharmaceutical industry, PJ is used as a base investigated. material in a variety of topical ointment formulations to minimize various skin diseases. Its occlusive, as Layered double hydroxides (LDHs) are synthetic well as healing characteristics render this substance anionic clay minerals represented by the molecular x+ − particularly efficient against dry and damaged skin [2, formula M (1−x) M3x (OH)2) . (A )x. nH2O where M2, - 3]. Because of its lipophilic character, physical and M3 and A represent divalent, trivalent cations and chemical inertness, PJ is also used as an essential anions respectively [14]. They have well-ordered ingredient in many formulations of cosmetic products brucite like layer structure in which the cations are providing different types of skin care and protection octahedrally coordinated by six oxygen atoms as 2+ 3+ by minimising friction or moisture loss or by hydroxides. The substitution of the M with M ions functioning as a grooming aid [4]. imparts a net positive charge to the sheets which are compensated by exchangeable interlayer anions and PJ is chemically similar to mineral oil. While mineral water [15]. The intrinsic hydrophilic surface property oil contains mainly liquid hydrocarbons, PJ is a of LDHs can be modified through surface mixture of solid and liquid hydrocarbons (normal, iso modification or intercalation with anionic surfactants and ring paraffins) in the form of 3D gel structure and [16-19]. Organo-LDHs are oil compatible hence is in a solid state at room temperature [5]. PJ is hydrophobic organic compounds and hence could be thus considered as a soft microcrystalline wax with used as phase stabilizers and rheology modifiers in oil high oil content [6]. Although PJ is petroleum (fossil rich formulations. Focke et al. [20] showed strong fuel) based product, components derived from shear thinning behaviour and anomalous temperature synthetic sources can be added to overcome its dependence of jojoba oil containing stearic acid drawbacks such as greasiness and resistance to intercalated Mg-Al-LDHs. Naime Filho et al., [21] washing in cold soap and detergent solutions [7,8]. incorporated glycine or alanine modified LDHs into a However, in such formulations, obtaining the desired silicone matrix containing Dimethicone, PEG-8 stability, viscosity and 3D-network structure phosphate (PE-100) and obtained a drastic change in formation remain a challenge. Disruption of 3D- the rheological behaviour, due to an extensively network structure causes liquid components to developed gel-like structure for the nanocomposite separate from the heavier components leading to an derivatives. While shear-thinning nature was evident, unstable formulation. In such cases, ingredients the critical concentration was observed to be 5% that can act as binders are required to obtain a suggesting the presence of a largely developed stable formulation [8,9]. interface between the filler and the polymer. The increase in viscosity was explained by the rather The incorporation of synthetic additives can greatly strong attrition phenomenon between amino acid alter the rheological properties of PJ itself which is anions and the silicone chains. very crucial in deciding the quality and function of final products in cosmetics where PJ is used as a main Inspired by these early investigations, the objective of or supportive ingredient. The problems such as liquid this work is to study the effectiveness of stearic acid separation, lack of structure and required viscosity modified layered double hydroxides (OLDH) as a could be related to the poor dispersion of the internal binder/stabilizer in PJ formulation and to evaluate phase as well as the degree of shear sensitivity of PJ shear flow properties of corresponding formulations. formulation [9]. There have been many studies to The interest is to develop an improved PJ composition investigate the rheological properties of PJ during past in terms of flow properties, stability as well as colour decades [3, 10-12]. However, only a little attention and feel of the product on the skin. has been given to PJ compositions containing additives that could have great impact on its The use of organic modified layered double performance characteristics. The use of synthetic wax hydroxides (OLDH) in PJ products is largely components such as Fischer-Tropsch wax in unknown. OLDH is expected to provide petrolatum formulation that can alter the rheological multifunctional benefits such as thickening, a 3D- properties and hence the skin sensation has been network structure, prevention of phase separation, reported recently [13]. US patent 3852475 [7] colour and consistency through interaction of organic
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surface layer with oil phase of the formulation. The Table 1. Composition of PJ formulations fact that no reference to OLDH in petroleum jelly formulations could be found in literature indicates that Entry Ingredients Percentage (%) the process and the product are unique. 1 Mineral oil Q.S. 2. EXPERIMENTAL 2 Microwax 10-27 3 OLDH 0.1-2.0 2.1 Materials 4 Paraffin wax 10-25
Hydrotalcite (Pural MG 70) of chemical formula 5 Amka wax 1
Mg2xAl2(OH)4x+4CO3.nH2O was supplied by Sasol Germany (referred to as LDH), which was 2.2.3 Characterization of OLDH synthesized by hydrolysis of hetero-metallic alcoholates. Stearic acid was supplied by Bio-zone X-ray diffraction (XRD) studies were conducted using chemicals, Kempton Park, South Africa. Distilled an X’Pert PRO X-ray diffractometer (PANalytical, water was used in all experiments. Other chemicals Netherlands) operating with Cu K-α radiation used were sodium dodecyl benzene sulphonate (Fluka (wavelength of 0.15406 nm) at 45 kV and 40 mA. The exposure time and scan speed for the XRD 98%), ammonium hydroxide (25%, Sigma Aldrich) o mineral oil and microwax (Akulu, South Africa), measurements were 19.7 min and 0.036987 /s, paraffin wax (Sasol, South Africa), Amka wax respectively. The presence of stearate moieties on (Amka, South Africa). LDHs was confirmed by Fourier transform infra-red spectroscopy (Perkin-Elmer Spectrum 100 2.2 Methods spectrometer, USA) with the MIRacle ATR attachment and a Zn/Se plate. A small amount of sample was pressed onto the Zn/Se plate and spectra 2.2.1 Synthesis of organically modified LDH over the range of 550 to 4000 cm-1 were collected. (OLDH) Morphological characteristics of neat LDH and
OLDH were obtained using scanning electron The surfactant assisted intercalation method [19] was microscopy (JEOL, JSM 7500F, Japan) at 3-kV used for the organic modification of LDH. In a typical acceleration voltage. Thermogravimetric analysis of procedure, 50 g LDH, 33.3 g stearic and 40 g of neat LDH and OLDH was performed using sodium dodecyl benzene sulphonate were suspended thermogravimetric analyzer (TGA, TA instruments, in 1.5 L de-ionized water. The mixture was heated to model Q500, USA). The temperature was ramped at 80°C for 8 h and allowed to cool overnight. The pH of -1 the mixture was kept above 10 using ammonium 10C min in air, from 25C to 900C. The stearic hydroxide. Two additional portions of stearic acid acid loading capacity of LDH was determined from (33.3g) were added in second and third cycle. The the residue weight percentage analysis. mixture is further allowed to stir for 8 h at 80 °C and then cooled slowly to ambient temperature. The 2.2.4 Rheological measurements sample was recovered by centrifugation and washed several times with water, ethanol and acetone to The steady and dynamic state rheology properties of remove excess stearic acid. PJ formulations containing different concentrations of OLDH and neat PJ were measured on an Anton Paar 2.2.2 Preparation of PJ formulation containing MCR501 rheometer using parallel plate geometry OLDH (PP50) with the gap set at 1.15 mm. The sample was placed at the centre of the stationary plate. In steady To a weighed mineral oil in a beaker specific state measurements, the shear rate was increased from concentration of OLDH was added and mixed with 0.01 to 100 s-1 and the flow curves were obtained high shear mixer (silverson, USA) at 2000 rpm for 2-3 under isothermal condition (26°C). In dynamic mode, minutes. This was followed by the addition of micro amplitude sweep was performed to determine the wax, paraffin wax and finally Amka wax. All the linear viscoelastic region as well as the flow point ingredients were mixed with spatula for 1-2 minutes (yield) of the samples. The angular frequency was set and heated to 75-80°C, while continuously stirring to at 6.28 rad/s and the strain varied from 0.01- help the waxes dissolve faster. The mixture was left to 200%. The frequency-sweep tests were carried cool down about 40°C. After packing, the sample was out by varying the angular frequency between 0.1 sent for stability and rheology testing. Table 1 shows and 100 rad s-1 at a fixed strain of 0.002%. the constituents of the formulations used in the current The samples were kept at rest for 2 min before study. A series of formulations were prepared by shearing and all experiments were carried out in varying the amount of OLDH. triplicates.
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3. RESULTS AND DISCUSSIONS (2 = 5.06) are in agreement with bilayer arrangement of carboxylic acids as per the previous 3.1 Characterization of OLDH reports. According to Xu and Braterman [26], the slant (contact/tilt) angle of the intercalated fatty acid Fig. 1 shows the X-ray diffractograms for neat LDH anion can be calculated using the equation, d = 1.48 + and OLDH. LDH shows sharp reflections at 2 = 0.26(n−2) sin where d is the d-spacing n is the 11.65°, 23.28° and 35.05°, due to (003), (006) and carbon number in the stearate chain, is the slant (009) diffraction planes respectively. The (003) angle of stearate anions. As per this equation, the tilt reflection at 2 = 11.65° corresponds to the basal angle of stearate anion in this case is calculated to be spacing close to 0.78 nm that is typical of highly 62, which is in close agreement with the reported crystallized LDH structure [22]. The basal spacing is value of 61 by Itoh et al. [25]. The existence of composed of an Al-bearing brucite-like octahedral characteristic peaks of pristine LDH in OLDH shows layer whose thickness and interlayer spacing is that the intercalation of stearate ions was not complete influenced by the size and alignment of the interlayer and it rather shows co-existence of unmodified LDH anion [23]. Assuming the brucite-like layer thickness minor phase with different interlayer spacing. This of approximately 0.48 nm as reported by Miyata et al. observation is agreement with Eshwaran et al. [27] [24], the interlayer spacing can be calculated as 0.3 who proposed the presence of pristine and intercalated nm which is in good agreement with the spacing of phases of Zn-Al LDH-stearate nanohybrid. 2- the CO3 intercalated Mg-Al-LDH. To substantiate XRD results, FTIR analysis of LDH However, a shift of LDH peaks to lower 2 was and OLDH was done and the spectra are compared in observed in the case of OLDH which is indicative of Fig. 2. The neat LDH showed a broad band in the -1 intercalation of stearate anions in to LDH inter layers. range of 3400–3500 cm which is attributable to –OH The sharp and symmetric peaks indicate highly stretching vibrations of the intercalated water ordered structure in OLDH. The modification of LDH molecules and octahedral layer of LDH [28,29]. The -1 with stearate ions increased the clay interlayer band in the range 1650-1600 cm is assigned to the distance from 0.78 nm to 5.23 nm, suggesting bending vibration from the interlayer water. The intercalation and self-assembly of stearate anions presence of carbonate anion is confirmed by the -1 within the interlayer space [25]. The reflections at characteristic peaks observed at 850–880 cm , 1350– -1 -1 5.23 nm (2 = 1.7), 2.61 nm (2 = 3.4) and 1.74 nm 1380 cm , and 670–690 cm [18]. The bands
(003)
(003) a.u.)
Intensity (a.u.) Intensity 1 3 5 7 9 11 13 15 2 theta (deg) Intensity ( Intensity b a
0 10 20 30 40 2 theta (deg)
Fig. 1. XRD spectrum of (a) Neat LDH (b) OLDH
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3.5 3.5
2916 3 3 1470 1540 2.5 2850 2.5 1360 2 3472 2
1.5 1428 1.5 a Absorbance Absorbance 1 1 1578 1638 0.5 b 0.5 1112
0 0 3550 3050 2550 2050 1550 1050 550 1700 1500 1300 1100 900 700 -1 Wavenumber (cm-1) Wavenumber (cm )
Fig. 2. FTIR spectrum of (a) Neat LDH (b) OLDH recorded at low-frequency region of 400–700 cm−1 [36]. Whereas, the steric acid intercalated LDH hybrid correspond to the vibration of M-O bond in the materials shows larger platelet and retained the brucite like lattice that is typical of this kind of hexagonal structure with coarse or irregular surface layered solids [30,31]. For OLDH, additional bands at morphology. This may indicate that the intercalation 2918 cm-1 and 2850 cm-1 appeared which are process involves dissolution and recrystallization of attributed to asymmetric and symmetric stretching the neat LDH to LDH-organo materials [18,37]. vibrations of –CH2- group of the alkyl chain of Furthermore, the change in crystal size morphology stearate anion respectively [32]. The presence of shows that the intercalation process was followed by bands at 1638, 1578, and 1540 cm-1 is related to recrystallization process. asymmetric while the bands at 1470, 1428 cm-1 are associated to symmetric stretching vibrations of TGA and DTG curves of neat LDH and OLDH are carboxylate (COO-) anion which confirms the shown in Fig. 4. A continuous mass loss in four stages intercalation of the stearate anions into the interlayer is observed in the thermograms till 500C after which region of LDH [33]. The intensity of the peak at 1360 a plateau is reached. The thermal decomposition of cm-1 gives an indication of the degree of exchange of unmodified LDH showed four decomposition steps the carbonate anion by stearate anions, of which in related to loss of physically adsorbed and interlayer this case significantly reduced showing replacement water molecules (50-150C), dehydroxylation of carbonate anion with stearate ions in the interlayer (190C), a combination of dehydroxylation- region [34]. However, the presence of low-intensity decarbonation reaction (306C) and oxidative carbonate peak in OLDH indicates that with stearic degradation of anions attached to LDH within acid modification, complete removal of carbonate interlayer (394C), respectively [38]. OLDH showed anion from the interlayer space was not achieved. additional decomposition peaks which may be According to Anbarasan et al. [35], this might be due attributed to the decomposition of intercalated stearate to the high charge density of LDH layers and rapid ions. The residual weight percentage comparison of uptake of CO2 by water molecule from atmosphere LDH and OLDH suggest that the total organic leading to re-substitution reactions. This result is in component in OLDH is approximately 30%. agreement with the XRD spectrum of OLDH where the existence of neat LDH as minor phase impurity 3.2 Rheological Properties of PJ Containing was evident. OLDH and Its Relevance to Real Life Application Fig. 3 shows the SEM images of the neat LDH and LDH-St hybrid. The neat LDH (Fig. 3(a)) had Fig. 5 presents the steady state shear viscosities of hexagonal plate-like morphology. Generally, the neat standard PJ and PJ formulations containing varying LDH exhibits hexagonal platelet morphology at the concentrations of OLDH. In steady state rheology micro scale resulting in the preferential growth of ab measurement, the sample is exposed to increasing faces (i.e., perpendicular to the stacking direction rotational shear stepwise and the viscosity of the
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sample is measured as a function of shear rate. The particles and the polymer chains in the wax where viscosity curves thus obtained represent the flow OLDH forms a 3D network structure that acts as a behaviour of the sample over a wide range of shear barrier to the polymer flow. This network formation rate simulating the behaviour of the fluid under may hinder the relaxation of the hydrocarbon polymer different conditions (e.g. low shear rate simulate the matrix when subjected to increasing shear. Decrease sample at rest, while high shear rates simulate the in viscosity for formulation containing 2 wt.% ODH sample during application [39]. From Fig. 5, it is clear indicates possible aggregation of OLDH particles at that the initial viscosity of PJ formulations containing higher concentrations. OLDH is always higher than that of the standard PJ indicating that the OLDHs function as a thickening From Fig. 5 it is also clear that all the systems agent. The absolute value of initial viscosity observed including standard PJ show non-Newtonian behaviour for standard PJ and PJ formulation containing.05, 1, and the shear viscosity gradually decreases with 1.5 and 2 % OLDH are 221, 1610, 12900, 7200 and increase in shear rate demonstrating shear thinning 5000 Pa.s respectively which indicates highest which is the common flow behaviour of most of the thickening effect in system containing 1.5 % OLDH. cosmetic formulations. According to Park et al. [3], Increasing concentrations of OLDH up to 1.5 wt. % the shear thinning behaviour at high shear rate created 3D network structure thus resulting in higher guarantees a high degree of mixability and viscosities. Based on the report by Xu et al. [40] and spreadability during their processing and actual usage Sochi et al. [41] higher viscosity of OLDH systems (as well as in other pharmaceutical and cosmetic can be attributed to some strong interaction between products). The shear rate dependency of these
a b
Fig. 3. SEM images of (a) Neat LDH (b) OLDH
110 0.5 100 394 C) 90 ° 0.4 315 80 190 70 451 0.3 60 a 50 0.2
aining mass (%) mass aining 40 84 306 30 b (a) Rem 20 0.1 (b)
10 (%/ loss weight Derivative 0 0 0 200 400 600 800 1000 0 100 200 300 400 500 600 700 Temperature (°C) Temperature (°C)
Fig. 4. TGA and DTG curves of (a) Neat LDH (b) OLDH
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Fig. 5. Steady state shear viscosities of standard PJ and PJ formulations containing varying concentrations of OLDH as a function of shear rate formulations can be described by a well-known power which the structural strength decreases. The standard law (or Ostwald-de Waele) PJ showed very low shear stress when compared to other formulations with OLDH. The higher yield η(̇) = K̇ n-1 (1) stress observed for PJ formulations containing OLDH also indicate higher shelf life and storage stability of Where; η is the shear viscosity, is the shear rate, K is the products as reported by Brummer et al. [43]. It has the consistency index and n is the flow behaviour been observed that the hydrophobic nature of OLDH index [42]. Generally, Newtonian behaviour is has considerably enhanced the stability of PJ for the exhibited when n is equals to 1 whereas shear followed period of 6 months under different storage thinning behaviour is less pronounced as n tends to 1. conditions (results not shown). The smaller the value of n, the greater is the degree of shear thinning. The calculated values for n is Table 2. Calculated flow behaviour index for presented in Table 2 which indicate lower n values for standard PJ and PJ formulations containing all OLDH containing systems in comparison to OLDH standard PJ showing better spreadability of the new formulations on human skin. Sample I.D () = k̇ γ̇n-1 Yield Stress (Pa) Neat PJ 0.30 53.12 It is apparent from Table 2 that the new PJ 0.5 % LDH PJ 0.18 68.55 formulations containing OLDH exhibit a higher 1 % LDH PJ 0.17 132.5 magnitude of yield stress in comparison to the 1.5 % LDH PJ 0.1 239.1 commercial PJ and this is attributed to the 3D- network structure imparted by the presence of OLDH 2 % LDH PJ 0.05 212.1 that can exhibit a resistance to the flow. During PJ formulation preparation, when molten material is To gain some understanding of the microstructure of cooled, the 3D network is developed through the PJ formulations, dynamic oscillatory shear rheological interaction of lipophilic OLDH and hydrocarbon measurements were conducted in the linear phase by sorption mechanism. When sufficient shear viscoelastic region and the results are presented in stress is applied the 3D network breaks down, leading Figs. 6 a and b. In oscillatory sweep tests, the to shear thinning flow behaviour. The shear viscosity, measuring system moves back and forth over a range as well as yield stress of new PJ formulations, of frequency and amplitude. The given strain and increase with increasing the OLDH content up to 1.5 shear stress are used to calculate the storage modulus wt% and decline thereafter. This established the G' and loss modulus G". The storage modulus G' is a critical concentration of OLDH to be 1.5 wt% above value of the stored deformation energy in the system,
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1000000 1000000 Neat PJ G' Neat PJ G'' Neat PJ G' Neat PJ G'' 0.5% LDH PJ G' 0.5% LDH PJ G'' 0.5% LDH PJ G' 0.5% LDH PJ G'' 1% LDH PJ G' 1% LDH PJ G'' 100000 1% LDH PJ G' 1% LDH PJ G'' 1.5% LDH PJ' G' 1.5% LDH PJ G'' 100000 2% LDH PJ G' 2% LDH PJ G" 1.5% LDH PJ G' 1.5% LDH PJ G" 2% LDH PJ G' 2% LDH PJ G'' 10000
10000
1000 Modulus (Pa) Modulus Modulus (Pa) Modulus
1000 100 a b
10 100 0.01 0.1 1 10 100 0.01 0.1 1 10 100 Strain (%) Angular Frequency (1/s)
Fig. 6. Dynamic oscillatory rheological modulus of standard PJ and PJ formulations containing varying concentrations of OLDH as a function of a) strain b) angular frequency typical of elastic (solid part) portion of the sample needed for irreversible deformation which in turn which gives information about the reversible shows higher structural and storage stability of PJ deformation behaviour and structural stability of the formulations containing OLDH. In frequency sweep sample. The loss modulus G" represents the lost plots (Fig. 6b), the critical strain, for all the systems, deformation energy and therefore characterizes the G' dominates over G'' both at low and high viscous portion (liquid part) of the sample providing frequencies-typical gel-like (solid-like) behaviour and information about the irreversible deformation this shows both long and short term-sample stability behaviour. Oscillatory test generally starts with an of the samples and less chance of separation. amplitude sweep where strain is varied between 0.01% and 100% at the constant angular frequency. Naime Filho et al. [21] obtained a percolated non- We can use the plots of G' and G'' against strain to Newtonian flow in silicones by incorporating glycine identify the linear viscoelastic strain range (LVE) and alanine modified Mg-Al-LDH. They reported (where the sample structure is not destroyed by higher storage modulus for silicone-LDH composites applied strain/deformation). Frequency sweep is done with a percolation threshold between 2.5 and 5 wt% in the LVE range and is used to predict long (low of filler loading LDH against unmodified silicone. frequencies) and short term (high frequencies) They interpreted such behaviour by the exfoliation of behaviour of the sample. The ratio of G" and G' is modified fillers in silicone matrix that forms an called loss factor (tan) which gives further idea about extensive network through strong interfacial the sample structure [39]. interaction between the organic anions in LDH and silicone polymer chains. It could be that a similar Fig. 6a compares the storage (G’) and loss moduli mechanism occurs in our case with rheological (G’’) of neat PJ with PJ formulations containing evolution of OLDH containing PJ formulations. various OLDH concentrations. Evidently, for neat PJ, Through strong interaction between the organic at higher applied strains, G’’ predominated over G’ moieties present on LDH surface, the 3D network indicating fluid–like the behaviour of hydrocarbons. structure could be strengthened which further In OLDH based systems, at all concentrations except immobilizes the liquid hydrocarbons (normal and iso- 2 wt.% OLDH, G’ is higher than G’’ suggesting that paraffins) resulting with significant improvement in the rheological property of PJ is dominated by elastic storage modulus and viscosity [44]. This is further property imparted by solid phase rather than the substantiated by the presence of non-terminal viscous property. The LVE range representing the behaviour of the moduli in the OLDH containing PJ at elastic strength of the material is observed to be lower frequencies. As the shear rate increases the higher for OLDH systems in comparison to neat PJ microstructure can orient with flow direction thus which indicates that incorporation of OLDH helped to leading to shear thinning behaviour [45]. OLDH, form an internal structure through 3D network which is hydrophobic and that has surface organic formation. This could mean that higher force is groups can be considered as an excellent shape
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anisotropic nanomaterial that is able to stabilize the and cream formulations: steady shear flow oil phase via particle assembling and network behavior. Arch. Pharm. Res. 2010;33(1);141- formation. 150. 4. Wang YP, Wang MC, Chen YC, Leu YS, Lin In summary, it is identified that OLDH shows great HC, Lee KS. The effects of vaseline gauze promises as rheology modifier to traditional strip, merocel, and nasopore on the formation petroleum jelly formulations offering viscosity of synechiae and excessive granulation tissue enhancement as well as shear thinning behaviour in the middle meatus and the incidence of which is directly related to formulation stability, skin major postoperative bleeding after endoscopic feel and spreadability which are crucial for sinus surgery. J. Chin. Med. Assoc. 2011; preparation of cosmetic and pharmaceutical products 74(1);16-21. for topical applications. Additional tests on evaluation 5. Presting W, Keil G. Ein Beitrag zur of sensory properties are underway with the Strukturuntersuchung von Mineralfetten III. commercial partner. Zum Gebrauchswert von Vaselinen. Chem. Tech. 1936;8;36. 4. CONCLUSIONS 6. Pena LE, Lee BL, Stearns JF. Structural rheology of a model ointment. Pharm. Res. The objective of the study was to investigate the 1994;11(6);875-881. possibility of employing organically modified layered 7. Tarangul EV, US Patent 3852475; 1974. double hydroxides as a rheology modifier for petroleum jelly formulation through linear and non- 8. Bekker M, Webber GV, Jacobs C, Louw NR, linear rheological property measurement. The Montgomery NT, Van Rensburg VJJ. US. systematic characterization results from this study Patent Application No. 14/361,204; 2012. indicate that OLDH can act as an effective thickener 9. Longer MA, Ch'Ng HS, Robinson JR. for PJ formulations. Incorporation of 0.5 to 1.5 % Bioadhesive polymers as platforms for oral OLDH results in 10-fold increase in viscosity in controlled drug delivery III: oral delivery of comparison to the standard reference PJ formulation chlorothiazide using a bio adhesive polymer. J. with significant increase in yield stress. This is Pharm Sci. 1985;74(4);406-411. attributed to the 3D network formation of PJ 10. Boylan JC. Rheological study of selected hydrocarbons with the LDH particles through the pharmaceutical semisolids. J. Pharm. Sci. surface organic groups which enhance the resistance 1966; 55(7);710-715. to flow of polymer chains. Under mechanical shear, 11. Davis SS. Viscoelastic properties of non-Newtonian shear thinning behaviour is observed pharmaceutical semisolids I: Ointment bases. J. for PJ formulations containing OLDH which could Pharm. Sci. 1969;58(4);412-418. enhance skin feel and spreadability of the product. 12. Pandey P, Ewing GD. Rheological Non-linear rheological properties show dominance of characterization of petrolatum using a solid-like behaviour of the OLDH based formulations. controlled stress rheometer. Drug Dev. Ind. Based on the rheological properties, higher storage Pharm. 2008;34(2);157-163. stability (shelf life), primary and secondary skin feel 13. Bekker M, Webber GV, Louw NR. Relating on actual application onto human body or skin are rheological measurements to primary and predicted for OLDH based PJ formulations. secondary skin feeling when mineral‐based and
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